In general, piezoelectric ceramics are ABO3 perovskite metal oxides, such as lead zirconate titanate (hereinafter referred to as “PZT”). However, PZT contains lead as an A site element, and its effect on the environment is regarded as a problem. Thus, there is a demand for piezoelectric ceramics of lead-free perovskite metal oxides.
One known piezoelectric ceramic of a lead-free perovskite metal oxide is barium titanate. In order to improve the characteristics of barium titanate, materials based on barium titanate are being developed. PTL 1 and NPL 1 disclose materials having an improved piezoelectric property in which the A site of barium titanate is partly substituted by Ca and the B site is partly substituted by Zr. However, these materials disadvantageously have a Curie temperature as low as 80° C. or less and therefore cause depolarization and deterioration in piezoelectric property under a high-temperature environment, such as in a car in summer. Furthermore, these materials disadvantageously have a low mechanical quality factor and therefore tend to generate heat and, upon the application of an alternating voltage, cause depolarization.
PTL 2 and NPL 2 disclose materials in which the A site of barium titanate is partly substituted by Ca and to which Mn, Fe, or Cu is added. These materials have a higher mechanical quality factor than barium titanate but disadvantageously have a poor piezoelectric property.